Palettes

A palette is, at its simplest, a lookup-table of colors with their corresponding index that is utilized when displaying computer graphics. Palettes are either:

• Defined by the hardware (i.e. the palette used by the graphics hardware of the NES) or
• Embedded within a file-format or specific to a piece of software (such as a palette embedded within a GIF or 8-bit PNG)

Whilst palettes are common across all media, they are particularly common in games.

Game palettes

Early game formats would often make use of a palette for two primary reasons:

• The historical limits of graphics hardware meant that a full-spectrum of colors was not feasible or necessary.
• Palette's allow for greater compression of in-game assets and less processing-time when loading these assets or displaying them on screen.

Structure

Game palettes often comprise a the following chunks of data:

• The palette itself, usually containing 256 swatches, 3 bytes per color totaling 768 bytes in length. The 256 limit corresponds to the 8bpp mode (or 256 color mode) limitations of personal computers of the time.
• Any number of Blending tables, which store pre-computed transformations on a palette, such as shading or blending. The results refer back to an index in the palette itself.

The palette:

• Palettes are often stored as tuples (1 byte for the red, green and blue channel in sequence) or in planes (1 byte for the red component for each swatch, then 1 byte for the green, then 1 byte for the blue).
• Whilst RGB component ordering is conventional, the components are sometimes ordered differently.
• If the palette appears dimmer than expected, it might be using less bits per byte in one or all components. It was common to store components using 6-bits (0-63). These would need to be multiplied by 4 to map the components back to the expected range of 0-255.
• Often, the palette is the first chunk of data within the file.